Forums :: NEW! Web Resources :: Features :: Photo Gallery :: Vintage Radio Shows :: Archives
Support This Site: Contributors :: Advertise


It is currently Oct Tue 20, 2020 11:21 pm


All times are UTC [ DST ]





Post New Topic Post Reply  [ 8 posts ] 
Author Message
 Post subject: ROM image from HP 4261A LCR Meter
PostPosted: Jul Thu 11, 2013 1:02 am 
Moderator

Joined: Jan Thu 01, 1970 1:00 am
Posts: 2219
Location: Seattle, WA, USA
A friend asked me to dump the control ROM (P/N 1818-2272A) for the HP 4261A LCR meter and I figured I would post the image here so everyone would have access to it if needed. Please download this image and save it! I want it to be available 'forever'.

Since the ROM has 16 data lines I read it in two pieces. The first contains the data from what I am calling the 'high data lines'. These are pins 24,6,23,7,22,8,21 and 9 in that order. Just to be clear on the data order, if you were to replace the upper data lines with a standard ROM, you would connect pin 24 to Q0 on the standard ROM, pin 6 to Q1, etc. The second file contains the data from what I am calling the 'low data lines' which are 20, 10, 19, 11, 18, 12, 17, and 13, again in that order. Get the files at:

http://dasarodesigns.com/~medasaro/1818-2272A%20-%20Low%20Data%20Lines.bin
and
http://dasarodesigns.com/~medasaro/1818-2272A%20-%20High%20Data%20Lines.bin

There is also another ROM chip in this thing but, for fear of damage, I am not going to pull and read it until I need to.

-Matthew

_________________
If it ain't broken, you’re not trying hard enough...


Top
 Profile  
 
 Post subject: Re: ROM image from HP 4261A LCR Meter
PostPosted: Jul Thu 11, 2013 1:49 am 
Member

Joined: Mar Thu 12, 2009 2:20 am
Posts: 1513
Location: Dayton, OH
Allow me to recommend KO4BB's site as a backup.....

Since I can tell you right now, I'll never find the file when I need it otherwise.. :)

Thanks for the effort however.....

David


Top
 Profile  
 
 Post subject: Re: ROM image from HP 4261A LCR Meter
PostPosted: Jul Thu 11, 2013 2:15 am 
Moderator

Joined: Jan Thu 01, 1970 1:00 am
Posts: 2219
Location: Seattle, WA, USA
Thanks. I have tried posting there before but after I fill out the form the file dosen't appear in the archive. Is there some trick?

Matthew

_________________
If it ain't broken, you’re not trying hard enough...


Top
 Profile  
 
 Post subject: Re: ROM image from HP 4261A LCR Meter
PostPosted: Jul Thu 11, 2013 2:22 am 
Member

Joined: Mar Thu 12, 2009 2:20 am
Posts: 1513
Location: Dayton, OH
I think the last time I uploaded anything I did it via FTP.

Named the file appropriately when uploading, and sent Didier a message afterwords.

He does have to move them manually from the upload area to an appropriate download directory, so they're not immediately available.

David


Top
 Profile  
 
 Post subject: Re: ROM image from HP 4261A LCR Meter
PostPosted: Jul Thu 11, 2013 5:38 am 
Moderator

Joined: Jan Thu 01, 1970 1:00 am
Posts: 2219
Location: Seattle, WA, USA
I made a mistake the first time I uploaded these files. If you downloaded them please do it again and delete the ones you downloaded before. I am really sorry about this.

Also, I burned the images onto a pair of 2716 ROMs, wired it all up on a breadboard, and was able to make my HP 4261A work just fine that way (although I did notice much more glitching then with the original chip, presumably because the 2716 chips are faster.) Thus I have confirmed that the images are good and that there is nothing special about the original ROM that will prevent it from being replaced with standard parts.

Image

I plan to have some boards made that will allow a tiny drop-in replacement. When and if I get that done I will make a post about it.

_________________
If it ain't broken, you’re not trying hard enough...


Top
 Profile  
 
 Post subject: Re: ROM image from HP 4261A LCR Meter
PostPosted: Jul Fri 12, 2013 4:15 am 
Moderator

Joined: Jan Thu 01, 1970 1:00 am
Posts: 2219
Location: Seattle, WA, USA
I couldn't help myself. Here are the contents of the other ROM chip in the HP 4261A (P/N 1818-2271A). Same format as before.

http://dasarodesigns.com/~medasaro/1818-2271A%20-%20Low%20Data%20Lines.bin
and
http://dasarodesigns.com/~medasaro/1818-2271A%20-%20High%20Data%20Lines.bin

-Matthew

_________________
If it ain't broken, you’re not trying hard enough...


Top
 Profile  
 
 Post subject: Re: ROM image from HP 4261A LCR Meter
PostPosted: Jul Sun 14, 2013 3:50 am 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 6111
Location: Montvale NJ, 07645
That is awesome. Thanks for your effort.


Top
 Profile  
 
 Post subject: Re: ROM image from HP 4261A LCR Meter
PostPosted: Jul Thu 18, 2013 5:15 am 
Moderator

Joined: Jan Thu 01, 1970 1:00 am
Posts: 2219
Location: Seattle, WA, USA
The friend for whom I originally collected these ROM images asked me to design an adapter of sorts to replace the original ROM chip with a standard modern part which I thought was a great idea as set out to do. What follows is my design process and pictures of the results.

I have designed replacements for other obscure ROM chips in the past, most notably for the Commodore PET. However, this case was somewhat unique as the original chip has 16 data lines, thus requiring me to either find a modern 16-bit parallel flash or EPROM or use two 8-bit parts. To complicate matters, the original chip can't be too much taller then the original or it won't fit correctly in the LCR meter. This height requirement pretty much ruled out using an old-fashioned DIP EPROM and mandated that whatever parts I find fit easily in the footprint of the original, a 28-pin wide DIP. Looking at the various modern flash and EPROM products, it quickly became clear that the only thing I was going to find in a parallel 16-bit format was EPROM and all of the 16-bit EPROMs that I could find used a DIP or PLCC44 package, neither of which would fit in the footprint of the original. That left me with the option of using two 8-bit EPROM chips. I was hoping to find EPROMs in an SOIC package as that package is the smallest, but although they seem to have been made that way in the past, all the current production parts I could find were in PLCC or DIP packages which I didn't think would fit. However, after a bit of head-scratching I realized that if I turned a PLCC28 package sideways it would just barely fit between the pins of a wide DIP! Armed with this, I chose the smallest EPROM still in production, the 27C256, and proceeded to lay out a board which would adapt the pinout of the original part to the 27C256's. I felt kind of bad using only 2KBits of a 256KBit part, but at $1.50 each I could hardly complain.

For the pins I chose to use Mill-Max P/N 350-10-164-00-006000 headers which are expensive but are gold-plated like the original pin were and are the correct diameter to use in an IC socket without damage. What's more, they are just the right height that the EPROM chips can fit under them without running into the board, thus reducing the height of the entire adapter to just that of the PC board plus the chips. All that was left was to lay out the board which turned out to be pretty dense due to the number of pins I was trying to connect in a small area. As a result the power and ground leads got longer then I like so I added an 0.1uF capacitor between power and ground near each of the EPROM chips. After that it was just a matter of waiting for the parts, programming the EPROMs and soldering it all together.

Here is the top of the completed part:
Image

And the bottom:
Image

The new ROM chip fit like a glove and worked like a charm. Here it is installed on the display board:
Image

It should be noted that since both the display ROM (1818-2271A) and the control ROM (1818-2272A) use the same pinout my board can replace either one - it is just a matter of the code programmed into the EPROMs. Along the same lines, the same ROM pinout may have been used in other applications meaning that the boards might be able to be used to make replacement ROMs for other types of equipment as well. If you happen to run into another piece of gear which uses the same ROM pinouts, I would be very interested to hear about it.

Finally, I am making all my design materials available to the world. Please download the zip archive at the link below which contains a PDF of the schematic, a parts list, and the board layout and schematic in ExpressPCB format. While they are free for personal use and redistribution without charge, I retain copyright. Neither the designs nor the completed boards may be sold without my prior permission.

http://dasarodesigns.com/~medasaro/1818-227xA/1818-227xA.zip

-Matthew

_________________
If it ain't broken, you’re not trying hard enough...


Top
 Profile  
 
Post New Topic Post Reply  [ 8 posts ] 

All times are UTC [ DST ]


Who is online

Users browsing this forum: keith49vj3, mikekent and 21 guests



Search for:
Jump to:  


































-->


Privacy Policy :: Powered by phpBB